Question

What is the cause of permanent hardness of water?

Answer 1

Hint : Presence of ion impurities into water make them hard water due to which they are not able to form lather production with soap solution due to this reason hard water is not a suitable candidate for washing clothes, laundry and dyeing. Hard water causes deposition of crusts on the inner surface of boilers and hence decreases the working efficiency of boilers.

Complete Step By Step Answer:
Water is classified into hard water and soft water depending on its behaviour toward the soap solution. As we know soft water does not contain ion impurities hence it forms lather with soap solution on the other hand, hard water contains impurities of metal ions and do not produce any lather on treatment with soap water.
Some ions such as bicarbonate ions, sulphate ions and chloride ions of magnesium and calcium metal are majorly responsible for causing hardness of water.
On the basis of ease of removal of impurities present, hard water is further categorized into Temporary hardness and permanent hardness.
Permanent hardness of water is caused due to the presence of different ions like sulphate, chloride of calcium metal and magnesium metal. These metal ions are dissolved in the hard water. This type of hardness of water is not readily removed from water and requires intense procedure to remove all these impurities.
Permanent hardness of water is not caused by carbonate ions of calcium and magnesium because carbonate ions are easy to remove. Therefore, permanent hardness of water is also termed as carbonate free hardness.
Permanent hardness is removed by washing soda method, ion exchange method and by calgon’s process.

Note :
Temporary hardness is commonly known as carbonate hardness due to the presence of impurities of carbonate ions of calcium and magnesium.
Boiling of water and treating it with calcium hydroxide (CLARK’S METHOD) cannot remove the permanent hardness of water. These two methods are used to remove temporary hardness.